Transcript Elements, Compounds and Mixtures

Elements
consists of only one kind of atom,
 cannot be broken down into a simpler
type of matter by either physical or
chemical means, and
 can exist as either atoms (e.g. argon, Ar)
or molecules (e.g., nitrogen, N2).
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Compounds
consists of atoms of two or more different
elements bound together,
 can be broken down into a simpler type of
matter (elements) by chemical means (but not
by physical means),
 has properties that are different from its
component elements, and
 always contains the same ratio of its component
atoms. (can write a formula for compounds)
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Mixtures
consists of two or more different elements
and/or compounds physically intermingled,
 can be separated into its components by
physical means,
 often retains many of the properties of its
components, and
 different components are not bonded. (cannot
write a chemical formula for mixtures)
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Activity Time
You will be handed an envelope with
some cards. Each card has a term on it.
Organize the cards to form a diagram or
picture that links each of the terms.
 You have a few minutes to come up with
your idea.
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Does yours look similar to this?
What is a pure substance?
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A pure substance has a constant, defined
composition and cannot be separated into
simpler substances by physical means.
There are two types of pure substances,
elements and compounds.
 Elements are pure substances that are made of
only one type of atom. The periodic table is a
table containing all elements.
 Compounds are pure substances that are
made of more than one type of atom, and can
be decomposed or broken down into its
elements by chemical means.
What do I mean by “Physical
means”?
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Chromatography - To separate different colored dyes. The dyes travel up the
chromatography paper at different distances before they cannot remain in solution. The
more soluble dyes move further up than the less soluble ones, hence separating from
each other.
Distillation - to separate and collect a liquid from a solution of a soluble solid. The
solution is heated in a flask until the liquid boils. The vapor produced passes into the
condenser where it is cooled and condenses to a liquid. The pure liquid (distillate) is
collected in a beaker.
Evaporation - This method is suitable to separate a soluble solid from a liquid. If the
solution is heated, the liquid evaporates leaving the solid behind.
Fractional Distillation - This is a special type of distillation used to separate a mixture
of liquids. Different liquids boil at different temperatures. When heated, they boil off and
condense at different times.
Filtration - To separate an insoluble solid from a liquid. The solid remains in the filter
paper and the liquid goes through the paper into the beaker.
Decant - pouring a liquid off a solid
Magnets - if one compound of a mixture is magnetic you could use a magnet to
remove it.
Centrifuge - this separates mixtures really well if you cant filter or decant
AND THERE ARE MORE…This is just a few to get you started…
So, what are “chemical means”
of separation?
Chemical methods uses energy and a
new substance is formed in the process
 To chemically separate a substance, a
chemical change is required
 The breaking of bonds between atoms
occurs. Collection of the resulting
products can be difficult.
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What kinds of mixtures exist?
A mixture is composed of more than
one element and / or compound.
 Different mixtures of the same
substances can have different
compositions (i.e., a mixture of water
and sodium chloride may be 80% water
and 20% sodium chloride, or 20% water
and 80% sodium chloride.)
 There are two types of mixtures,
homogeneous and heterogeneous.
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Homogeneous mixture
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A homogeneous mixture
has the same composition of
elements and / or compounds
throughout.
If you observed a homogeneous mixture under
a microscope, you would see that the particles
of various components are evenly distributed.
A homogeneous mixture is also called a
solution.
Heterogeneous mixture
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A heterogeneous mixture has different regions or
areas with different compositions and properties.
The substances in a heterogeneous mixtures are
not evenly distributed.
We say that we can see “distinct phases” of matter
in a heterogeneous mixture (i.e. the ice cubes, the
soda and the straw would be three separate
phases in a glass of cold soda)
In contrast a suspension is a heterogeneous
mixture of larger particles. These particles are
visible and will settle out on standing. Examples of
suspensions are: fine sand or silt in water or
tomato juice
Here is how to “picture” the
particles in each…
What do each represent?
Mixture?
*Homogeneous?
*Heterogeneous?
Element?
Compound?
Practice what you know
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This link is to an interactive quiz
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Another link to an online quiz
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One more (only 5 questions!)
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A matching on-line game